Adding value to cosmogenic nuclide analyses: multi-metric approaches to studying landscape evolution

Chemical and physical weathering and subsequent erosion from hillslopes provide the raw materials for river transport and deposition. As such, active channel sediments and sedimentary archives such as alluvial terraces contain within them a record of catchment-wide weathering and erosion processes. Cosmogenic nuclides are regularly called on to measure denudation rates, which represent the sum these processes. However, in rapidly evolving landscapes cosmogenic nuclides provide insights into catchment-averaged weathering and erosion processes only over relatively short timescales. For example, in the Southern Alps of New Zealand, denudation rates can exceed 10mm/yr, implying cosmogenic nuclide averaging timescales of less than a century. Similarly, sediment yields also provide a geologically near-instantaneous picture of catchment-wide denudation. An interesting problem then arises in which it becomes challenging to separate the effects of long-term geologic drivers of weathering and erosion such as ongoing rapid uplift from those of recent low frequency/high magnitude geologic events or anthropogenic activity. In these rapidly evolving settings, soil profiles, sedimentary deposits and geomorphic form can be useful archives to disentangle these confounding factors. We combine cosmogenic nuclides with; elemental mass balance, grain size, U/Pb, and landscape morphology to interrogate the drivers (e.g., uplift) and constrain the rates of weathering and erosion across Aotearoa, New Zealand.